Frequently Asked Questions

What is Lisp?

Lisp---AKA, Common Lisp---is a member of the Lisp-family of programming languages that descends from the original LISP language proposed by John McCarthy in the 1950s. All Lisp-family languages share common features, such as the S-Expression syntax based on a subset of Lambda Calculus and Polish prefix notation, but Common Lisp in particular is known for its concise syntax, extensibility, multi-paradigm approach to programming, and rich macro system for code expansion.

Common Lisp is ANSI Standardized, actively supported in both commercial and open-source implementations, available for nearly every platform (coming to new ones all the time), has a lively community, and a large and actively maintained collection of user-contributed libraries.

Who should learn Lisp?

Complete beginners to programming, who want to be assured of learning a powerful language that will help them develop unique insights of their field. Someone who has struggled with programming before. Hobbyists, who are looking for a new challenge. Professional developers looking to take their performance and productivity to the next level. In a word, everyone.

Is Lisp as hard as people say it is?

No. Lisp is actually the simplest programming language, and has no syntactic cruft. While it wasn't designed to be "easy to learn" like Swift, Python, Ruby, or Basic, there is less overall to learn and you will be writing real, useful programs in Lisp sooner than you could with other languages.

What do I need to know before learning Lisp?

Lisp, like all other programming languages, requires a certain degree of advanced computer skills. You should be a strong typist, comfortable in a variety of text editors, and know how to use the command line to run text-based applications and compile software from source code. In addition, up-front familiarity with powerful programmer's text editors such as Emacs or VIM will help you be more productive through Lisp's incremental, interactive development cycle---but for now all you really need to know is how to enter text into a file, save it to disk, and run it from the command line.

How long does this book take to complete?

You should take as long as you need with each module to fully grasp the material. It's not a race, and the only deadlines are the ones you set for yourself.

Assuming you already have some programming experience and can do at least one module a day, you should expect to spend at least three months.

What do I need to learn Lisp with this book?

You will need a computer where you have the administrative rights to install software without anyone else's help. Pretty much any personal computer will do, Lisp runs everywhere, on Windows, macOS, Linux, UNIX, BSD, etc., as well as supporting mobile and embedded targets. Complete instructions for setting up your development environment on Windows, Linux, and macOS are included in this book.

What is Lisp used for?

Common Lisp is an ANSI standardized high-level, general purpose, dynamic, multi-paradigm, programmable programming language. So any application, script, or web site can be written in Lisp, generally in less time and with substantially fewer lines of code than could be achieved with other programming languages.

Some of the most exciting projects in the history of computing are being developed in Lisp right now. In fact, Common Lisp is still the most advanced, robust, expressive, and powerful programming language ever invented, giving it an edge both in everyday programming challenges as well as exploratory programming; and its ANSI standardization gives it a stability that no other language can match, meaning your code is far less susceptible to bit-rot over time.

Is Lisp a functional programming language?

This is a common misconception, but no, it is not. Functional programming is a style of writing code, a paradigm, based on the lambda calculus, where the programmer aims to eliminate side-effects and reduce software to mathematical purity. This means that a function is not permitted to change state outside of its lexical scope, and that if it is run multiple times with the exact same parameters, it will always return the same result.

Common Lisp is not a 'pure' functional language, however, such as Haskell; it is multi-paradigm like OCaml. You can choose to use the functional paradigm in Common Lisp if you like, but you can also use Procedural, Object-Oriented, Event-Oriented, novel new paradigms like Aspect-Oriented, or mix and match to your hearts content. Strict Functional programming languages do not offer this flexibility.

What kind of programs will I learn to write with this book?

In this book, we will be writing command-line applications, text-based adventure games, web applications, cross-platform desktop software, native apps for mobile devices, 2D and 3D games, as well as exploring advanced use cases in the industries that favour Lisp over other programming languages—specifically, enterprise, big data, financial services, natural language processing, robotics, space tech, artificial intelligence, neuroscience, quantum computing, cryptography/security, government and military, exploratory programming, and academic research applications such as computational physics.

What about other Lisp-family languages, like Scheme or Clojure? Will this site teach me them too?

The focus of this site is entirely on Common Lisp. While all Lisp-family languages share certain common features, such as the S-Expression syntax, Scheme and Clojure are very different languages than Common Lisp in practice. That being said, you will be better equipped to learn Scheme or Clojure after learning Common Lisp first, and have a better understanding of when Scheme or Clojure is a better choice for a specific project.

Is this site affiliated with Zed Shaw and Learn Code The Hard Way?

No. This is a separately run and managed site, based on the format of Zed Shaw's LxTHW open-source package for writing your own programming language book. You should check out the project and search online to see what others are up to! More information is available at: Learn Code The Hard Way.